Solvent extraction system



Filed July 15. 1942 Patented June 26, 1945 i 2,319,332 soLvENr Ex'raAc'noN SYSTEM Philip M. Arnold, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Application July 13, 1942, Serial No. 450,725

(Cl. 26o-.6815) 8 Claims.

This invention relates to a method whereby a monoolen and a dioleiin preferably having the same number of carbon atoms per molecule, can be separated from two streams of hydrocarbons in the vapor state, one of which contains the monoolen and which preferably consists essentially of paraiins and the monoolen, and the other of which contains the diolen and preferably consists essentially of the monooleiin and diolen.

In accordance with the invention the separation is accomplished by the use of a solvent, such as furfural, which is selective towards both monoolefins and diolefins, but more selective toward diolefins. First the monoolen-paraflln stream is treated with the selective solvent to extract the monooleiin from the paraiilns. The monoolefln-rich solvent from this extraction is used as the selective solvent for the diolefln in the diolen-monoolefln stream. The diolen from this latter stream displaces the monoolen from the selective solvent; thus a vapor phase rich in monoolen and a liquid extract phase rich in dioleiin are obtained. The diolen is then stripped from the selective solvent. One oi' the advantages of this arrangement is that only one stripping unit is required. If both streams were extracted with lean solvent, two strippers would be required, one for the extract from each stream.

This system o! extraction is particularly adaptable to the recovery of the monoand di-oleln obtained in the two-stage dehydrogenation of normal butane for the production of butadiene. since the eiiluents from the two stages consist essentially of a mixture of monoolen and normal parailln and of diolen and monooleiin, respectively, for the first and second stages. However. the invention may be applied to any two streams 'whatever their source or origin provided one consists essentially of a mixture of parain and monoolefin and the other of monooleiln and diolen.

The invention will be more readily understood tower wherein it is intimately contacted with furfural which enters near the top of tower 2 through line 5. Line 5 is supplied with furfural from lines 6 and I2. The furfural selectively dissolves the butylenes, thus separating them from the butanes.` The butanes leave tower 2 overhead by means of conduit 3 whence they mal7 be withdrawn from the extraction system via line 3A. The rich furfural leaves tower 2 via line 4 containing cooler 4A and enters the top of tower 1. A feed consisting of a mixture of butylenes and butadiene is introduced into tower 1 via line I0 below the level of introduction of the butylene-rich furfural. The butylene-butadiene stream is intimately contacted with the butylenerich furfural in tower 1. The furfural being more selective towards butadiene than toward butylenes tends to absorb the butadiene, thus separating it from the butylene in the butylenebutadiene stream. However, at the same time as the butylene-rich furfural selectively absorbs butadiene, the butylenes previously absorbed are displaced giving a butadiene-rich furfural. The butylenes leave tower 1 via line 8 whence they may beremoved from the extraction system via line 8A. The butadiene-rich furfural stream leaves tower 1 via line 9 to enter stripping column I I where the butadiene is stripped from the furfural. The butadiene leaves column II overhead via line I3 through cooler I4 and line I5 to enter reflux' accumulator I6.- The liquefied butadiene is withdrawn from the bottom of accumulator I6 by pump I8 through line I1. The butadiene is discharged from pump I8 through line I9. A portion of the butadiene is returned to column I I via line 20 as reflux. The remaining portion is withdrawn from the system through line 2 I. The lean furfural leaves column I I as a bottom product through line I2, passes through cooler I2A, and is 'returned to the extraction system through line 5.

Reboil arrangements (reboiling coils 2A, 1A and IIA) are employed in the two extraction steps and in the stripping zone. Furfural is a solvent to varying degrees for practically all hydrocarbons. Those hydrocarbons towards which furfural is least selective are most readily removed by reboiling, while those towards which it is most selective are more dimcult to remove by reboiling. In the rst step of the extraction process, wherein butylenes are selectively absorbed from butanes, a certain amount of butane will tend to dissolve along with the butylenes. This can be practically completely removed from the furfural by a reboiler arrangement 2A located in the bottom of the absorber 2. It is necessary to operate the reboiler 2A at such a temperature that a part of the butylenes will be displaced. However, these displaced gaseous products in passing upwardly through the furi'ural in the absorber come in contact with furfural which is colder than that inthe bottom of the absorber near the reboiler, and the furfural being more selective towards the butylenes again absorbs them while most of the butanes will be withdrawn overhead. 'I'he same process goes on in the second absorption step, wherein the butvlene-rich furfural from the first step is used as the selective solvent for butadiene contained in a butadiene-butylene stream. The butadiene tends to displace the butylenes from the butylene-rich furfural. but, r'levertheless,l without reboiling of the furfural small amounts of butvlene will remain dissolved in the furi'ural and later appear as a contaminant in the. butadiene. Conseauently. the residual butyleneg have to be removed in the same manner as described for the removal of the residual butanes bv a. reboil arrangement. It is obvious that a reboil arrangement IIA or its equivalent must be employed in the stripping column Il in order to recover the butadiene.

The invention. in a more specific aspect, may be applied to a process for the two-stage catalytic or thermal, preferably the former. dehydrogenation of normal butane to butadiene. For example. fresh normal butane fed via line 30, together with recycled butane from line 3. may pass into first-stage dehydrogenation zone 3i and the eflluent comprising mainly butvlene and unreacted butane. either directly as such or after separation in any way of a C4 fraction containing these components. passed via line 32 into line I. Likewise the butylenes leaving via line l may be passed, c

either alone or in admixture with fresh butylene feed entering via line 35, through the secondstage dehydrogenation zone and the dehydrogenation eiiiuent comprising chiefly butadiene and unreacted butylene, either directly or after separation of a C4 fraction comprising those components, passed via line 31 into the line Il. This arrangement gives an unusually simple, compact. eillcient and economical installation.

It will be understood that instead of the preferred selective solvent, furfural, I may use, tht ugh by no means absolutely eouivalently therewith in every respect, any other solvent having generally the solvent action described, such as: nitrobenzene, dichlorodiethylether, dimethyl formamide, methyl levulinate. glycol diacetate. diethyl acetamide pyridine, phenol, phenol plus water, benzyl alcohol, etc.

Instead of butadiene, other aliphatic coniugated diolefins such as isoprene. piperylene, certain of the hexadienes, etc. may be recovered by means of the process of my invention, from admixture with aliphatic monooleflns, usually of a corresponding number of carbon atoms. In such case a stream of the corresponding olefins in admixture with the corresponding paramns may be extracted with the selective solvent and the resulting olefin-rich solvent used to treat the diolen-monoolefin stream. For example a mixture of pentane and pentenes may first be extracted to selectively dissolve pentenes and the pentene-rich solvent employed to treat apentadiene-pentene stream in the manner described above.

Many advantages of my invention will be obvious to those skilled in the art. Among them are the fact that essentially pure bui'enes and butadiene are readily recovered from the corresponding streams containing the same in a simpler, more efiicient and more economical manner. Also the apparatus requirements are simplified, and operation is more trouble-free. The process is particularly valuable when combined with the two-stage dehydrogenation of normal butane to butadiene. The displacement of the butenes with butadiene may be nicely regulated so that neither the butene product nor the butadiene product is contaminated-with the other. Numerous other advantages will be apparent.

I claim:

l. The method of manufacturing butadiene from normal butane which comprises passing said normal butane through a first dehydrogenation zone to at least partially convert it to butylene, treating a stream containing the unreacted butane and butylene content of the effluent with a selective solvent which is selective for butylene and butadiene but more selective for the latter, to dissolve the butylene content of said stream, recycling the undissolved unreacted butane to said first zone, treating the butylene-rich solvent with a butadiene-butylene mixture derived from a second dehydrogenation zone to causethe butadiene to dissolve in said solvent and displace the butylene therefrom, and passing the butylene derived by said last step to a second dehydrogenation zone to at least partially convert it to butadiene.

2. In a process for preparing butadiene from normal butane wherein said normal butane is dehydrogenated at least partially to butylene in a first stage and wherein said butylene is at least partially dehydrogenated to butadiene in a second stage, the improvement which comprises treating the butylene-butane content of the firststage eiiluent with a selective solvent for butylene and butadiene, and desorbing butylene from the butylene-rich solvent by contacting with the butadiene-butylene content of the second-stage eiiluent whereby the butadiene displaces the dissolved butylene.

3. The process of claim 2 wherein said solvent is furfural.

4. The method of separating a monoolefin from a first hydrocarbon stream containing the same and a close-boiling parailin hydrocarbon and also separating an essentially monoolefin-free alt phatic conjugated diolefln from a second hydrocarbon stream containing the same and from a different source than said first hydrocarbon stream, which comprises extracting said first stream by intimately contacting same in a first zone with a lean selective solvent which is more selective towards both monoolefins and dioleflns than parailin hydrocarbons and is more selective towards diolens than the monoolefins and thereby effecting selective dissolution of substantially all of the monooleiin content of said stream while allowing the paramn hydrocarbon content thereof topass through said first zone undissolved, withdrawing saidundissolved paraiiin from said fine zone, extracting said second stream by intimatelyv contacting same in a second zone with the monoolefin-rich solvent resulting from said extracting step and thereby eiiecting selective dissolution of the diolefln content of said second stream and displacement by said diolefln of substantially ailof said dissolved monoolefin from said monoolefin-rich solvent, recovering said displaced monoolen, and withdrawing same from said second zone and from the system as the monooleiin product of the process, and

stripping said dissolved dioleiin essentially free from monooleiin from the diolen-rich solvent resulting from said second extracting step and withdrawing the diolen so stripped and eseentially free from monoolen from the system as the diolefin product of the process.

5. The method of separating an essentially parafiin-free monoolen from a first hydrocarbon stream consisting essentially of said monoolen and the orresponding parafiin and also separating an essentially monoolen-free aliphatic conjugated dioleiin from a second hydrocarbon stream from a different source than said first hydrocarbon stream consisting essentially of said dolefin and the corresponding monoolen which has the same number of carbon atoms as said monoolen in said first stream which comprises extracting said first stream by intimately contacting same in a rst zone with a lean selective solvent which is more selective towards both monooleiins and diolens than' paraillns and is more selective towards diolefins than monoolens and thereby effective selective dissolution of substantially all of the' monooleiin content of said stream while allowing the paraffin content to pass through undissolved, withdrawing said undissolved parafiin from said rst zone, separately extracting said second stream by intimately contacting same in a second zone with the monoolefin-rich solvent resulting from s'aid extracting step and thereby eiiecting selective dissolution of the dioletin content of said second stream and displacement of substantially all ot said dissolved monoolen from said monoolen-rich solvent while allowing the monoolen content of said second stream to pass through undissolved, in admixture with said displaced monoolen, recovering said undissoived and displaced monoolen in admixture and withdrawing same from said second zone and from the system as the monoolen product of the process and stripping said dissolved dioleiin essentially free from monooleiin from the dioleln-rich solvent resulting from said second extracting step and withdrawing the diolefln so stripped and essentially free from monoolen from the system as the dioleiln product of the process.

6. The process of claim 5 in which the rich solvent leaving said extracting steps is reboiled immediately prior to its exit therefrom to insure complete removal of parain from the monooiefin-rich solvent leaving the first extracting step and complete removal of monooleiln from the diolefin-rich solvent leaving the second extracting step.

'7. The process of claim 5 in which said paraffin is butane, said monoolen is butylene and said diolefin is butadiene.

8. 'I'he process of claim 5 in which said parafiin is butane, said monoolen is butylene, said diolefin is butadiene, and said solvent is furfural.

PHILIP M. ARNOLD. 

